The present invention relates generally to watermarking of digital signals, and more particularly to the provision of digital watermarks based on host-matching codes. Such watermarks are used, for example, to hide information in an audio or video signal without degrading the quality of the audio or video output.
Digital watermarks are auxiliary signals embedded into a host signal in such a way that they are substantially imperceptible during standard usage of the host signal, but detectable by specially designed watermark extractors. Typical host signals are audio and video signals, images, faxes, computer files, and the like. A typical objective of watermarking is to provide copy protection for the content contained in the host signal. Other applications of digital watermarks include broadcast monitoring, host-signal integrity verification, entertainment, and the like.
A number of distinct prior art watermarking technologies have been proposed and patented. These technologies achieve different levels of transparency (fidelity, or non-perceptibility), robustness to standard host-signal processing, tamper resistance, implementation cost, throughput (watermark data rate), false positive rate, and layering potential. Typically, it is possible to trade one of the listed properties for another. For example, by changing the amount of inserted signal (a.k.a. watermark strength) it is possible to trade transparency for robustness. Many proposed techniques use error-correction-codes to trade throughput for robustness, which could be traded further for transparency.
It would be advantageous to provide a technique that can be used to trade throughput directly for transparency, and indirectly for robustness. It would be further advantageous to provide such a technique that is more efficient than using error-correction-codes. The methods and apparatus of present invention provides these and other advantages, as more fully described below.